This work is an investigation of the control of rDNA transcription in mammalian liver by the use of in vivo pharmacologic intervention to alter transcript ion with subsequent analysis of such alterations in vitro. Alterations in both structural components of the transcriptional complex and the dynamics of transcription are to be examined. Protein phosphorylation and and ADP-ribosylation, in vitro, will be examined for their ability to produce the same types of changes seen after in vivo intervention. Development of a molecular based model for control of rDNA transcription is targeted in these studies.